Year in review: Critical Care 2004 - nephrology

A comprehensive analysis and annotation of human normal urinary proteome

Biomarkers are measurable changes associated with the disease. Urine can reflect the changes of the body while blood is under control of the homeostatic mechanisms; thus, urine is considered an important source for early and sensitive disease biomarker discovery. A comprehensive profile of the urinary proteome will provide a basic understanding of urinary proteins. In this paper, we present an in-depth analysis of the urinary proteome based on different separation strategies, including direct one dimensional liquid chromatography–tandem mass spectrometry (LC/MS/MS), two dimensional LC/MS/MS, and gel-eluted liquid fraction entrapment electrophoresis/liquid-phase isoelectric focusing followed by two dimensional LC/MS/MS. A total of 6085 proteins were identified in healthy urine, of which 2001 were not reported in previous studies and the concentrations of 2571 proteins were estimated (spanning a magnitude of 10⁶) with an intensity-based absolute quantification algorithm. The urinary proteins were annotated by their tissue distribution. Detailed information can be accessed at the “Human Urine Proteome Database” (www.urimarker.com/urine).

Procalcitonin cannot be used as a biomarker of infection in heart surgery patients with acute kidney injury

PURPOSE

We intended to assess how acute kidney injuy impacts on procalcitonin levels in cardiac surgery patients, with or without infection, and whether procalcitonin might be used as a biomarker of infection in acute kidney injuy.

MATERIAL AND METHODS

A case-control study was designed which included patients that had had cardiac surgery between January 2011 and January 2015. Every patient developing severe sepsis or septic shock (n = 122; 5.5%) was enrolled. In addition, consecutive cardiac surgery patients during 2013 developing systemic inflammatory response syndrome (n = 318) were enrolled. Those recruited 440 patients were divided into 2 groups, according to renal function.

RESULTS

Median procalcitonin levels were significantly higher during the 10 postoperative days in the acute kidney injury patients. Regression analysis showed that postoperatory day, creatinine, white blood cells and infection were significantly (P < .0001) associated to serum procalcitonin level. In patients with creatinine ≥2, median procalcitonin levels were similar in infected and non-infected patients. Only when creatinine was less than 2 mg/L, the median procalcitonin levels were significantly higher in patients with infection, as compared to those with no infection.

CONCLUSIONS

In acute kidney injuy patients, high procalcitonin levels are a marker of acute kidney injuy but will not be able to differentiate infected from non-infected patients.

Calculating evidence-based renal replacement therapy - Introducing an excel-based calculator to improve prescribing and delivery in renal replacement therapy - A before and after study

BACKGROUND

Transferring the theoretical aspect of continuous renal replacement therapy to the bedside and delivering a given "dose" can be difficult. In research, the "dose" of renal replacement therapy is given as effluent flow rate in ml kg^-1h^-1. Unfortunately, most machines require other information when they are initiating therapy, including blood flow rate, pre-blood pump flow rate, dialysate flow rate, etc. This can lead to confusion, resulting in patients receiving inappropriate doses of renal replacement therapy. Our aim was to design an excel calculator which would personalise patient's treatment, deliver an effective, evidence-based dose of renal replacement therapy without large variations in practice and prolong filter life. Our calculator prescribes a haemodialfiltration dose of 25 ml kg^-1h^-1 whilst limiting the filtration fraction to 15%.

METHODS

We compared the episodes of renal replacement therapy received by a historical group of patients, by retrieving their data stored on the haemofiltration machines, to a group where the calculator was used. In the second group, the data were gathered prospectively.

RESULTS

The median delivered dose reduced from 41.0 ml kg^-1h^-1 to 26.8 ml kg^-1h^-1 with reduced variability that was significantly closer to the aim of 25 ml kg^-1.h^-1 (p < 0.0001). The median treatment time increased from 8.5 h to 22.2 h (p = 0.00001).

CONCLUSION

Our calculator significantly reduces variation in prescriptions of continuous veno-venous haemodiafiltration and provides an evidence-based dose. It is easy to use and provides personal care for patients whilst optimizing continuous veno-venous haemodiafiltration delivery and treatment times.

How Robust are our Methods of Detecting Impaired Glomerular Filtration Rate in the Intensive Care Unit?

BACKGROUND

Serum creatinine is not a sensitive marker to assess early loss of renal function in acute kidney injury. Timed creatinine clearance and several formula used to predict glomreular filtration rate have not been validated.

METHODS

In a prospective observational study in 50 adult patients admitted to the intensive care unit with apparent normal renal function, we assessed the glomerular filtration rate by the formula methods and timed creatinine clearance.

RESULT

The mean serum creatinine was 0.77mg/dl, SD ± 0.15 (range 0.5-1.14 mg/dl). The mean measured creatinine clearance was 87.15 ml/min/1.73m(2), SD ± 20.5 (range 56.9-137 ml/min/1.73m(2)). In 25 (50%) patients, one hour urinary creatinine clearance was <80 ml/min/1.73m(2) and in two (4%) patients, the creatinine clearance was <60 ml/min/1.73m(2). Spearman correlation coefficient and regression analysis revealed a statistically significant correlation for the Cockcroft-Gault and predictive equations when compared with measured creatinine clearance. The differences between the predictive equations and creatinine clearance, as illustrated by the ±95% confidence interval in the Bland-Altman graphs was very significant [Cockcroft- Gault = -40.3 to 17.7 ml/min/ 1.73m(2), Modification of Diet in Renal Disease equation = -46.2 to 30.6 ml/min/1.73m(2) and the simplified Modification of Diet in Renal Disease equation = -72.8 to 24.8 ml/min/1.73m(2)].

CONCLUSION

Formula methods and creatinine clearance are more sensitive than serum creatinine in detecting early phase of acute kidney injury. However, there is no agreement between these methods of glomerular filtration rate estimation.

Ascertainment and epidemiology of acute kidney injury varies with definition interpretation

BACKGROUND AND OBJECTIVES

Differences in defining acute kidney injury (AKI) may impact incidence ascertainment. We assessed the effects of different AKI definition interpretation methods on epidemiology ascertainment.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Two groups were studied at Texas Children's Hospital, Houston, Texas: 150 critically ill children (prospective) and 254 noncritically ill, hospitalized children receiving aminoglycosides (retrospective). SCr was collected for 14 d in the prospective study and 21 d in the retrospective study. Children with known baseline serum creatinine (bSCr) were classified by the pediatric Risk, Injury, Failure, Loss, End-Stage Kidney Disease (pRIFLE) AKI definition using SCr change (pRIFLE(DeltaSCr)), estimated creatinine clearance (eCCl) change (pRIFLE(DeltaCCl)), and the Acute Kidney Injury Network (AKIN) definition. In subjects without known bSCr, bSCR was estimated as eCCl = 100 (eCCl(100)) and 120 ml/min per 1.73 m(2) (eCCl(120)), admission SCr (AdmSCr) and lower/upper normative values (NormsMin, NormsMax). The differential impact of each AKI definition interpretation on incidence estimation and severity distribution was evaluated.

RESULTS

pRIFLE(DeltaSCr) and AKIN led to identical AKI distributions. pRIFLE(DeltaCCl) resulted in 14.5% (critically ill) and 11% (noncritical) more patients diagnosed with AKI compared to other methods (P 0.05). Different bSCr estimates led to differences in AKI incidence, from 12% (AdmSCr) to 87.8% (NormsMin) (P 0.05) in the critically ill group and from 4.6% (eCCl(100)) to 43.1% (NormsMin) (P 0.05) in the noncritical group.

CONCLUSIONS

AKI definition variation causes interstudy heterogeneity. AKI definition should be standardized so that results can be compared across studies.

Urine neutrophil gelatinase-associated lipocalin is an early marker of acute kidney injury in critically ill children: a prospective cohort study

Introduction

Serum creatinine is a late marker of acute kidney injury (AKI). Urine neutrophil gelatinase-associated lipocalin (uNGAL) is an early marker of AKI, where the timing of kidney injury is known. It is unknown whether uNGAL predicts AKI in the general critical care setting. We assessed the ability of uNGAL to predict AKI development and severity in critically ill children.

Methods

This was a prospective cohort study of critically ill children. Children aged between 1 month and 21 years who were mechanically ventilated and had a bladder catheter inserted were eligible. Patients with end-stage renal disease or who had just undergone kidney transplantation were excluded. Patients were enrolled within 24 to 48 hours of initiation of mechanical ventilation. Clinical data and serum creatinine were collected daily for up to 14 days from enrollment, and urine was collected once daily for up to 4 days for uNGAL measurement. AKI was graded using pRIFLE (pediatric modified Risk, Injury, Failure, Loss, End Stage Kidney Disease) criteria. Day 0 was defined as the day on which the AKI initially occurred, and pRIFLEmax was defined as the worst pRIFLE AKI grade recorded during the study period. The χ² test was used to compare associations between categorical variables. Mann-Whitney and Kruskal-Wallis tests were used to compare continuous variables between groups. Diagnostic characteristics were evaluated by calculating sensitivity and specificity, and constructing receiver operating characteristic curves.

Results

A total of 140 patients (54% boys, mean ± standard deviation Pediatric Risk of Mortality II score 15.0 ± 8.0, 23% sepsis) were included. Mean and peak uNGAL concentrations increased with worsening pRIFLEmax status (P < 0.05). uNGAL concentrations rose (at least sixfold higher than in controls) in AKI, 2 days before and after a 50% or greater rise in serum creatinine, without change in control uNGAL. The parameter uNGAL was a good diagnostic marker for AKI development (area under the receiver operating characteristic curve [AUC] 0.78, 95% confidence interval [CI] 0.62 to 0.95) and persistent AKI for 48 hours or longer (AUC 0.79, 95% CI 0.61 to 0.98), but not for AKI severity, when it was recorded after a rise in serum creatinine had occurred (AUC 0.63, 95% CI 0.44 to 0.82).

Conclusion

We found uNGAL to be a useful early AKI marker that predicted development of severe AKI in a heterogeneous group of patients with unknown timing of kidney injury.

Year in review 2005: critical care--nephrology

We summarize original research in the field of critical care nephrology accepted or published in 2005 in Critical Care and, when considered relevant or directly linked to this research, in other journals. The articles have been grouped into four categories to facilitate a rapid overview. First, physiopathology, epidemiology and prognosis of acute renal failure (ARF): an extensive review and some observational studies have been performed with the aim of describing aspects of ARF physiopathology, precise epidemiology and long-term outcomes. Second, several authors have performed clinical trials utilizing a potential nephro-protective drug, fenoldopam, with different results. Third, the issue of continuous renal replacement therapies dose has been addressed in a small prospective study and a large observational trial. And fourth, alternative indications to extracorporeal treatment of ARF and systemic inflammatory response syndrome have been explored by three original clinical studies.